A typical catalytic converter includes a metal or ceramic substrate treated with a noble metal catalyst enclosed in a stainless steel casing made, for example, out of ASTM 409 stainless steel. A temperature-resistant and shock-absorbing ceramic or wire mesh mat is used to retain the substrate in the casing.
Many catalytic converters have a fusion welded clam shell half type casing to retain the substrate and mat in place. Other catalytic converters have tubular sections with various cross-sectional shapes and transition ends fusion welded in place. Still other catalytic converters have tubular sections with transition ends ram formed to the required dimension. While the ram forming technique is cost effective, it presents rather severe size limitations and, more specifically, ram forming offers a limited range of feasible tubular diameter reduction ratios.
Referring to FIG. 1, an example known catalytic converter 9 includes a tubular stainless steel shell 13 encasing a catalytic converter substrate 11, which is encircled by a mat (not shown). The stainless steel shell 13 has, welded at its ends, transition pieces 15, each typically comprising a stamped member including a generally conical portion 17 and a generally cylindrical portion 19. The cylindrical portion 19 is welded (or clamped) to the exhaust system of the vehicle.
Referring to FIGS. 2-5, an example known spin forming machine 33 is shown. The spin forming machine 33 includes stand 55 with a single or plurality (three, as shown in FIGS. 2 and 3) of forming rollers 25 rotatively attached thereto. The rollers 25 each have a tapered face 27 and are equally distant from a common axial centerline. The spin forming machine 33 has a mandrel 35 to internally support a tubular metal piece 29 to be operated on.
The spin forming machine 33 is supported on a platform 37. The piece 29 and/or stand 55 is rotated and, depending upon the material used for piece 29, the piece 29 is heated while the platform 37 is indexed toward the piece 29. FIG. 3 illustrates the initial outer diameter 51 of the piece 29. As the roller tapered faces 27 make contact with the piece 29, the diameter of the portion of the piece 29 in the machine 33 is reduced to an outer diameter 53 shown in FIG. 4.
To achieve the amount of tapered reduction desirable in many types of articles, such as a catalytic converter to replace the converter shown in FIG. 1, two or more machines 33 applying two or more reduction steps to the piece 29 are necessary.